The device can be installed on any Luger pistol equipped with a hold open device, such as those guns produced in Germany during the years 1908 to 1942 and known as Model P.08.
In such model, the user is alerted to the fact that the gun has fired the last round from the magazine by the toggle's remaining in open, or buckled, position when the magazine has been emptied and the remaining shell in the firing chamber has been fired and ejected.
Heretofore, in order to restore the toggle assembly to closed position, it has been necessary to press the magazine release stud, remove the empty magazine from the butt of the pistol, grasp and forcefully pull up and back on the milled toggle knobs as far as the breech block will go and then release the knobs so that the recoil spring can drive the breech block straight ahead in its guide into locked position.
Gun collectors and fanciers appreciate the watch-like, or camera-like, precision of Luger pistols; but would often prefer that the toggle be selectively returnable to base position, once it has performed its warning function, by a simpler, more direct course of action than that recited above.
It is likewise most desirable to be able to release the toggle and simultaneously lock the trigger mechanism in the unlikely but possible event that the toggle prematurely remains in open position as a result of a weak or malfunctioning hold open catch spring.